Effect of grinding variables on the NH4HCO3 –dtpa soil test values for Fe, Zn, Mn, Cu, P, and K

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Abstract
The effect of grinding force, time, and weight of soil on the NH4HCO3 ‐DTPA extractable levels of Fe, Zn, Mn, Cu, P and K from 10 Colorado soils were studied. It was found that the amount of extractable iron and zinc increased, with an increase in force or time of grinding. The significant interaction between time and force of grinding indicates that the combined effect of the larger force and the longer time in increasing the extractable levels of Fe and Zn was greater than the additive effects of these factors. The weight of soil being ground had a small effect on extractable Fe (significant at 10% level) and no effect on other elements. Extractable levels of Mn, Cu, P, and K were not affected by the grinding treatments. Iron was increased 112% and zinc was increased 44% due to the combined effects of the larger force and the longer time of grinding in soils averaging 12.8 and 1.1 ppm in Fe and Zn, respectively. It is concluded that grinding variables should be standardized, otherwise interlaboratory comparisons and standardized interpretations of results are not possible.